The present invention relates to an improvement of an ignition timing adjusting device for controlling the ignition timing of an internal combustion engine to minimize the nitrogen oxide content of exhaust emission (hereinafter described simply as NOx emission).
Conventionally proposed in such an ignition timing adjusting device of this type as disclosed in the U.S. Pat. No. 3,735,743. With this conventional device, the function of a conventional vacuum ignition advancer is retarded to temporarily retard the ignition timing of the engine during the period of transitional driving when acceleration and deceleration are repeated, and then the normal or usual timing is maintained at a cruising speed of the vehicle. However, in this conventional device, the response of the vacuum ignition advancer is merely retarded at the advancing side and the response in the retarding side is not considered. This indicates that there is a limit to decrease the Nox emission at a low speed after the vehicle starts.